This invention relates to admixtures for use in extrudable hydraulic compositions, and extrudable hydraulic compositions which are extrudable into hardened parts having a satisfactory strength and surface smoothness.
In traditional hydraulic compositions for extrusion molding, asbestos were used as additive fibers for facilitating extrusion into hardened parts having surface smoothness. In the recent years, the amount of asbestos used drastically decreased due to health considerations and legal regulations. At present, pulp fibers are often used as the substitute. In unison with this tendency, nonionic water-soluble cellulose ether is commonly used for the purposes of improving the dispersion of pulp fibers, enhancing strength properties and facilitating extrusion.
As the avoidance of asbestos is in progress, the amount of pulp fibers used is increasing. From the fire resistant standpoint, pulp fibers should be used in a minimum amount sufficient to provide necessary shape retention and flexural strength. Since flexural strength is preferential in most cases, the amount of pulp fibers used is in excess of the necessity to provide shape retention. Additionally the increased amount of pulp fibers undesirably detracts from the surface smoothness of hardened parts.
An object of the present invention is to provide an admixture for use in extrudable hydraulic compositions, which permits the hydraulic composition containing a less amount of pulp fibers to be extruded into hardened parts having necessary flexural strength and satisfactory surface smoothness; and an extrudable hydraulic composition comprising the admixture.
The inventor has found that when a nonionic water-soluble cellulose ether having a transparency of 35 to 89% in a 2 wt % aqueous solution at 20xc2x0 C. is added as an admixture to a hydraulic composition containing a less amount of pulp fibers, the resulting hydraulic composition is extrudable into hardened parts having flexural strength and satisfactory surface smoothness.
Accordingly, the invention provides an admixture for extrudable hydraulic compositions, comprising a nonionic water-soluble cellulose ether having a transparency of 35 to 89% in a 2 wt % aqueous solution at 20xc2x0 C.; and an extrudable hydraulic composition comprising the admixture.